Prismatic plate



June 5, 1962 K. FRANCK ETAL 'PRISMATIC PLATE F'ild May 21, 1957 2 Sheets-Sheet 1 IJJ HH E r INVENTORS A/UPT FlP/INCK V542; S. W/NC m %& ram

KTTORNEYS United States Patent i 3,038,065 PRISMATIC PLATE Kurt Franck and Vearl S. Wince, Newark, Ohio, assignors to Holophane Company, Inc., New York, N.Y., a corporation of Delaware Filed May 21, 1957, Ser. No. 660,678 7 Claims. (Cl. 240-106) The present invention relates to a prismatic plate or light transmitter.

The invention provides a light transmitter or panel which can be readily manufactured and has a 'very light weight so that it may be easily supported, particularly from a ceiling. The plate or panel may, for example, be formed of a single piece of molded plastic material. The panel can be used with other similarly shaped panels to cover an extended ceiling area, as is usually required for fluorescent lamps. In such case, the panels are adapted to be mounted below the fluorescent lamps and form a substantially continuous surface for completely obscuring the fluorescent lamps and preventing glare. As shown in our copending application, Serial No. 645,315, filed March 11, 1957, now abandoned, the panels are adapted to be included in a totally closed fixture for fluorescent lamps and to be readily mounted and removed. As further shown in the above mentioned application, the panels may have various shapes, such as circular, polygonal, or rectangular and be provided with peripheral stiffening flanges with coplanar edges to form a recess which is crossed by strengthening ribs intersecting one another in order to stiifen the plate against deformation. The lower surface of the plate is covered with light, redistributing prisms to alter the direction of the transmitted light and prevent glare.

The invention is particularly concerned with the shape and arrangement of the prisms, which are preferably in the form of cones, for obtaining uniform average brightness in different directions. The cones, or most of them, are formed so as to have substantially square bases. It has been found that with such cones the brightness control is best across the edges of the squares and worst across the corners of the squares. This means that a plate having all cones oriented similarly, will at some viewing angles have a brightness control which is quite different from that at other angles of view. It is desirable to average the best performance and the worst performance of the cones in such a way that from any lateral angle of view, the performance is about the same. This objective is obtained according to the invention, by arranging about half of the cones squarely, that is so that the edges of their bases run, say, transversely and longitudinally, and arranging the other half of the cones so that their base edges are diagonal. In such an arrangement the first mentioned cones show best control in the direction in which the diagonally arranged cones show least control, and vice versa, averaging out the brightness control quite effectively. These two types of cones are preferably arranged in blocks or groups of rows and the very fact that they have different brightness values at the same angle of view enhances the lighted appearance of the plate by giving it life and sprarkle, whereas an overall pattern of cones arranged, say, squarely all over the plate tends to be monotonous and lifeless. Further, one of the blocks of cones may be provided with small rhombic shaped. prisms which emphasize the rows of cones adding further sparkle and distinctive appearance to the cone arrangement.

The object of the invention is to provide a light transmitter in the form of a transparent plate having an arrangement of prisms or cones which provides a fairly uniform amount of average brightness control in different ice lateral directions and yet has a considerable amount of sparkle and freedom from monotony.

Gther objects and advantages of the invention will become apparent and the invention will be fully understood from the following description and drawing in which:

FIG. 1 is a perspective view of a light transmitter;

FIG. 2 is a plan view of the bottom part of the light transmitter;

FIG. 3 is an enlarged detailed view of the portion of the light transmitter included in rectangle 3 of FIG. 2;

FIG. 4 is a sectional view taken along the line 44 of FIG. 3;

- FIG. 5 is a sectional view taken along the line 5-5 of FIG. 3;

FIG. 6 is a detailed view showing the cones and prism arrangement;

FIG. 7 is a sectional view taken along the line 77 of FIG. 6;

FIG. 8 is a sectional view along the line 8-8 of FIG. 6;

FIG. 9 is an enlarged detailed view showing another cone arrangement;

FIG. 10 is a sectional view taken on the line 10-10 of FIG. 9; and 1 FIG. 11 is a sectional view taken on the line 11-11 of FIG. 9.

Referring to the drawing, a light transmitter 10 may have a web consisting of two upwardly sloping panels or plates 11 and 12. The web is provided with downwardly etxending peripheral flanges 13-16 so that the web and the flanges form a recess. The recess is crossed by strengthening ribs 17 and 18 extending between opposite flanges. The bottom edges of ribs 18 and the flanges lie in the same horizontal plane. The bottom faces of plates 11 and 12 are covered with prismatic elements which will be described in connection with FIGS. 3 and 6 to 11. The bottom edges of ribs 17 and 18 are provided with prisms 19 and the bottom edges of the flanges 14 and 16 are provided with prism-s 20. These prisms extend crosswise to the ribs and flanges and serve to prevent glare when the transmitter is viewed in directions along the ribs and flanges. 'The transmitter 10, either alone or in conjunction with other light transmitters, may be supported from a ceiling under fluorescent lamps as shown and described in our above-mentioned copending application. Although the transmitter is here illustrated as having a square configuration, other shapes may, of course, be used.

For the purpose of further obscuring the lamps which may be mounted above the light transmitter 10, ribs '17 and 18 are provided with vertical flutes '21 and 22 on both sides thereof and the flanges -14 and 16 are provided with similar flutes on their inner sides.

The entire bottom surface of plates 11 and 12, is covered with cones and prisms. The cones are arranged in two series of groups of parallel rows 23 and 24. The cones intersect each other so that they have approximately square bases. The edges of the bases of the cones 25 ex tend in diagonal directions while the edges of the bases of cones 27 and 28 extend transversely and longitudinally and these cones will be referred to as the square cones, whereas the cones 25 will be referred to as the diagonal cones. The cones project outwardly from the bottom surface of the plates. Between the cones 28 there are provided prisms 30 having flat sides 31 and 32 and a rhombic base. Prisms 30 project downwardly from the bottom surface of the plate forming a-ridge having an apex 33. Substantially half of the prisms are of the diagonal type and half are of the square type. The purpose of this arrangement of the cones is to obtain a better average brightness control. It has been found that brightness control is best across the edges of the squares and worst across the corners of the squares. This means that in a plate having cones arranged in squares, brightness control would'be quite different at some angles of view from that at other angles of view, if all of the cones or prisms were oriented in the same way. This would be undesirable. By arranging about half of the cones diagonally while leaving the other half in the square arrangement, the brightness control is averaged in such a way that from any lateral angle of view, the brightness control is about the same. In other words, with an arrangement of this type, where the square cones show best control, diagonally arranged cones show least control, and vice versa, averaging out the brightness control quite efiectively. At the same time, the very fact that the diiferent blocks or rows of cones have different brightness values, at the same angle of view, enhances the lighted appearance of the plate by giving it variety and sparkle, while an overall pattern of cones oriented entirely in one way, tends to be monotonous and lifeless. The rhombic prisms 30 further emphasize the rows of cones adding further sparkle and distinctive appearance to the cone arrangement.

FIGS. 9 to 11 show a modified cone arrangement. Here again, the cones are arranged in alternate groups of rows 46 and 44. The apices of cones 45in adjacent rows 43 are staggered and their bases are oriented diagonally, whereas the cones 48 in row 44 are oriented squarely, that is, the edges of their bases are generally in transverse and longitudinal directions, as shown in the drawing. The arrangement differs essentially from that of FIG. 6 in that the rhombic prisms 30 are omitted, otherwise, the arrangement shownin \FIGS. 9 to 11 functions similarly to the cone arrangement shown in FIGS. 3 and 6.

It will be understood that plates having the cone arrangements disclosed herein, may be used as light transmitters for various applications and that the plates may have any desirable shape or contour. Many variations and modifications of the particular arrangements herein illustrated will be apparent to those skilled in the art, and therefore, the invention is notto be construed as limited except as defined in the following claims.

We claim:

1. A light transmitter for use with horizontal fluorescent lamps comprising a horizontal transparent plate having on one face spaced groups of parallel contiguous rows of discrete protruding prisms having pointapices and second groups of parallel contiguous rows of discrete protruding prisms having point apices, the second groups of rows occupying the spaces between the first groups of rows, the prisms of the first and second rows covering substantially the entire area of said face, the projections of the bases of the prisms of the firstrows on a plane parallel to the plate having edges which extend at acute angles to the directions of said first rows, the projections of the bases of the prisms of the second rows on a plane parallel to the plate having edges which extend perpendicularly and parallel to the direction of said'second rows,

whereby the prisms of the first and second rows give different amounts of brightness control in a given azimuthal direction but together have an average brightness control which is approximately the same at all viewing angles.

2. A light transmitter as in claim 1 wherein said projections of the bases of the prisms of the first and second rows are substantially square.

3. -A light transmitter as in claim 2, wherein said projections of the bases of the prisms of the first rows extend at angles of substantially 45 to the direction of the rows. i 4. A light transmitter for a fluorescent lamp fixture comprising a horizontal transparent plate having on its bottom face a first series of spaced substantially parallel rows of prismatic cones and a second seriesof substantially parrallel rows of prismatic cones occupying entirely the spaces between the rows of the first series, said cones projecting outwardly from said one face, the sides of the cones intersecting at their bases so that the bases of the cones of the first rows and second rows are in plan view of substantially square outline, the edges of the outlines of the bases of the cones in the first series of rows extending diagonally to the edges of the outlines of the bases of-the cones of the second series of rows.

5. The light transmitter of claim 4, wherein the edges of the outlines of the bases of the cones of the first series of rows extend at angles of 45 to the direction of the rows and the outlines of the bases of the cones of the second series of rows have edges which extend substantially-parallel and perpendicularly to the direction of the rows.

6. A light transmitter including a horizontal plate of transparent plastic material, said plate including outwardly extending prismatic cones on its bottom face, the sides of the said prismatic cones intersecting at their bases so that when viewed in plan, said sides present substantially polygonal base outlines, the base outlines of some of the prismatic cones having edges extending diagonally with respect to the edges of the base outlines of the other prismatic cones, whereby the differences and brightness control of the'prismatic cones at different azimuthal viewing angles is averaged out and the brightness control is made more uniform.

7. A light transmitter as set forth in claim 6 wherein said polygonal base outlines of some of said prismatic cones are substantially square.

References Cited in the file of this patent UNITED STATES PATENTS 595,273 Soper Dec. 7, 1897 944,348 Schrader Dec. 28, 1909 1,194,294 Johanson Aug. 8, 1916 1,370,885 Frederick et al. Mar. 8, 1921 1,950,560 Martinek et al Mar. 13, 1934 2,161,842 Allison June 13, 1939 2,309,038 'Biller Jan. 19, 1943 2,558,422 De Leo June 26, 1951 

